This was a piece written by Yoshimi Yamada Maples, for a person in the Western States who would like to practice Japanese calligraphy. It is written in the Kaisho style.
全汝形，抱汝生，勿使汝思慮營營。
Literally, this means: "Perfect you form, protect your life; do not let your thoughts be agitated"
Thomas Merton, the translator whose version you cite, is taking a bit of liberty with the text. The Chinese is more terse.
The Thomas Merton translation is
"Hold your being secure and quiet. Keep your life collected in its own center."
Meanings of individual character is
全 【ぜん】 (n) (1) all; whole; entire; complete; overall
汝 【い; しゃ】 (n) (arch) (vulg) you
形 【かた; がた】 (n,suf) (1) (がた when a suffix) (See 型・1) shape; appearance; (2) collateral; (3) (See 銭・ぜに・1) obverse of an old "zeni" coin
抱え 【かかえ】 (n) (1) armful; (2) employee
生 【せい; しょう】 (n) (1) life; living; (n,n-suf) (2) (せい only) (male) (hum) I; me; myself
勿れ【なかれ】 (prt) must not; do not
使 【し】 (n) (1) messenger; (2) (abbr) (See 検非違使) police and judicial chief (Heian and Kamakura periods); (3) {Buddh} (See 煩悩・2) klesha (polluting thoughts such as greed, hatred and delusion, which result in suffering)
思う To think
思慮 【しりょ】 (n,vs) prudence
營Unknown in Japanese
